Descramble That DVD in 7 Lines

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Descramble That DVD in 7 Lines

CAMBRIDGE, Mass. – Descrambling DVDs just got even easier, thanks to a pair of MIT programmers. Using only seven lines of Perl code, Keith Winstein and Marc Horowitz have created the shortest-yet method to remove the thin layer of encryption that is designed to prevent people – including Linux users – from watching DVDs without proper authorization.

Their "qrpff" program is a more compact cousin of the DeCSS utility that eight movie studios successfully sued to remove from the website of 2600 Magazine. But unlike DeCSS, qrpff is abbreviated enough for critics of the Motion Picture Association of America to include in, for example, e-mail signature files – and many already have.

"I think there's some value in demonstrating how simple these things really are and how preposterous it is to try to restrict their distribution," says Winstein, a 19-year-old MIT sophomore computer science major.

Winstein says it's folly for MPAA and its allies to try to restrict a 526-character program that can be handed out on business cards. "I'm showing the humor in trying to call these seven lines on a piece of paper a device," he says.

The probable spread of qrpff on business cards, on T-shirts, and bumper stickers closely resembles the distribution of encryption code in signature files and T-shirts a few years ago. Such civil disobedience flouted U.S. export laws in a kind of global keep-away game.

Winstein and Horowitz, an MIT alumnus, are both members of the MIT Student Information Processing Board, the university's social group for programmers and like-minded folks. They jointly developed qrpff for a two-meeting seminar that Winstein taught earlier this year.

Unlike some other DVD-descramblers, qrpff doesn't include the necessary five-byte title key – such as 153 2 8 105 225 – which must be given to the program so it can perform the necessary decryption.

That, says Winstein, means qrpff doesn't violate the Digital Millennium Copyright Act, which the movie studios used in a federal lawsuit against 2600. "Even if whatever is enjoined by that injunction in New York is a violation of the law, I think there's a reasonable case to be made that my seven lines of Perl isn't," Winstein says.

The code takes advantage of a Perl command called eval, which evaluates the program text when it is executed:

In a brief filed last month, the Bush administration sided with the movie industry against DeCSS, saying that software is not speech-protected by the First Amendment but can be regulated like parts to a machine: "This function is entirely nonexpressive, and thus does not warrant First Amendment protection."

U.S. District Judge Lewis Kaplan ruled last August that DeCSS was like a "common-source outbreak epidemic" that violated the law's prohibition against circumventing copyright-protection technology. The DMCA prohibits anyone from publishing or publicly distributing any hardware or software that "is primarily designed or produced for the purpose of circumventing protection afforded by a technological measure that effectively protects a right of a copyright owner."

David Touretzky, a scientist in the computer science department at Carnegie Mellon University who testified for the defense, has included qrpff in his gallery of DVD descramblers. The gallery is designed to highlight the problem of dividing computer code into expressive and functional categories: It includes descramblers written in C, Scheme, English, and even haiku.

Last month, the MPAA demanded that Touretzky take down his page. He responded: "I would like to know if it is the intent of the MPAA to exert editorial control over scholarly publications by computer science faculty that deal with DeCSS, and if so, exactly which sort of publications will the MPAA permit in the future, and which sort will result in legal threats such as your letter of yesterday."